Time-course of object detection and categorization in fragmented object contours K Taniguchi1, T Tayama1, S Panis2, J Wagemans2 |
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1Department of Psychology, Hokkaido University, Japan |
| In order to investigate the temporal dynamics of different perceptual decisions, we measured performance (RT and accuracy) in a detection and three categorization tasks (Natural and Artifactual categorization, superordinate-level categorization and basic-level categorization) using fragmented object contour stimuli taken from Panis, De Winter, Vandekerckhove and Wagemans (2008). We manipulated fragment length (short versus long) and fragment type (curved versus straight), and measured the complexity of the overall shapes, to study how these visual factors influence the time to take a decision in each task by analyzing the shape of the RT distributions using event history analysis. In all tasks, the main effects of stimulus length and complexity were significant for fast responses, consistent with the idea that fast responses are based on early representations following bottom-up processing. For short fragments and slower responses, we found a hazard advantage for curved versus straight fragments when the task was basic-level recognition, consistent with the idea that late responses reflect top-down influences from activated high-level candidate representations on visual grouping processes during difficult recognition. These findings suggest that the top-down influence in object recognition is dependent on the abstraction level of the category. |
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